1. Field of the Invention
The present invention relates to an electronic cassette for radiographic imaging.
2. Description of the Related Art
Radiographic imaging apparatuses, which capture radiographic images of objects by irradiating the objects with radiation (for example, X-rays) and detecting the intensity distributions of X-rays transmitted through the objects, are known and widely used in the medical and industrial fields. Two methods of radiographic imaging are available, namely, a film/screen method and a CR method. These methods use photosensitive films or phosphor plates which retain images as latent images, such films or plates being stored in storage cases called film cassettes, which are standardized under JIS Z 4905 (referred to herein as “document 1”). In some cases, a radiographic imaging apparatus is used, which uses a DR (Digital Radiography) method using a flat panel detector (referred to herein as an “FPD”) formed from a thin-film semiconductor material on an insulating substrate. A cassette used for radiographic imaging based on such DR method is referred to herein as an “electronic cassette”.
In general, radiographic imaging apparatuses are installed and used in a so-called radiation room. With recent advances in packaging techniques, a low-profile, light-weight portable electronic cassette has been commercialized to allow quicker imaging of wider regions of an object, and an electronic cassette which achieves a reduction in thickness and weight while withstanding specified loads has been proposed (see Japanese Patent Laid-Open No. 2005-195643 (referred to herein as “document 2”)).
There are various kinds of bases such as stands for standing positions and tables for lying positions, which are used to position cassettes relative to objects (such as a human body or part thereof) in accordance with desired imaging forms. Many of these bases are designed in conformity with the outer shapes of film cassettes having the standard sizes defined in document 1. If an electronic cassette for radiographic imaging based on the DR method does not conform to a standard size, it is necessary to introduce a new base when introducing a radiographic imaging apparatus based on the DR method. This extra equipment increases the investment cost. It is therefore required to provide a radiographic imaging apparatus (electronic cassette), based on the DR method, which has almost the same outer shape as that of the film cassette standardized in document 1. For this purpose, with advances in high-density packing techniques and wireless techniques, an electronic cassette having an outer size compatible with the standard size of a film cassette has been proposed (Japanese Patent Laid-Open No. 07-140255 (referred to herein as “document 3”)). An electronic cassette having the same size as that of a standardized film cassette can be held in various kinds of existing bases formed in conformity to a film cassette size. Therefore, it is possible to introduce an imaging apparatus based on the DR method while minimizing the necessary investment in new equipment.
When making an electronic cassette with almost the same dimensions as those of a film cassette whose outer dimensions are standardized according to document 1, since the outer size includes a margin of about 15 mm around an imaging region, electric components are disposed on the rear surface side of the FPD. It is therefore necessary to dispose the FPD and electric components in the thickness direction within the thickness of the cassette, that is, 15 mm. This makes it necessary to design an electronic cassette in consideration of the influence of electrical noise on images due to low-profile high-density packaging.
Imaging techniques using an electronic cassette include imaging performed while the electronic cassette is placed on a soft surface, such as a bed in a hospital ward. The object to be imaged is then placed on the cassette and imaging is performed while the local load, such as that from the head or extremities of a person that are the object being imaged is imposed on the electronic cassette. In such an imaging technique, since the body weight of the patient directly acts on the electronic cassette, the cassette is required to have high rigidity. In addition, since a technician carries the electronic cassette to an imaging position, the electronic cassette itself is required to be light weight. Therefore, the electronic cassette is required to have almost the same outer shape as that of a film cassette with a standard size while being both robust and light weight, whilst being designed internally so as to address the issue of deterioration in image quality due to noise or the like described above. Documents 2 and 3, however, give no consideration to challenges associated with these requirements.